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REPORT OF THE GROUND WATER RESOURCE ESTIMATION

COMMITTEE

GROUND WATER RESOURCE ESTIMATION METHODOLOGY

Ministry of Water Resources Government of India

NEW DELHI 2009

FOREWORD

Ground water has emerged as an important source to meet the water

requirements of various sectors including the major consumers of water like

irrigation, domestic and industries. The sustainable development of ground water

resource requires precise quantitative assessment based on reasonably valid

scientific principles. The Ground Water Estimation Committee- 1984 till now

formed the basis of ground water assessment in the country. The ground water

development programme implemented in the country was also guided by ground

water resource availability worked out from this methodology. The experience

gained in last more than one decade of employing this methodology supplemented

by number of research and pilot project studies has brought to focus the need to

update this methodology of ground water resource assessment. The National Water

Policy also enunciates periodic assessment of ground water potential on scientific

basis. The Ministry of Water Resources, Govt. of India, therefore, constituted a

committee consisting of experts in the field of ground water to recommend a

revised methodology. This report is the final outcome of the recommendations of the

committee.

The revised methodology as recommended has incorporated number of

changes compared to the recommendations of Ground Water Estimation Committee -

1984. In this methodology, watershed has been adopted as the assessment unit in

hard rock areas. Ground water assessment has to be made separately for non

command and command areas and areas of poor quality of ground water have to be

treated separately. Ground water recharge has to be assessed separately for

monsoon and non monsoon seasons. An alternative methodology has been provided

for estimation of specific yield based on application of ground water balance in dry

season which would be applicable in the non command part of hard rock areas.

Norms for return flow from irrigation are now based on the source of irrigation i.e.

ground water or surface water, type of crops, and depth to water table below ground

level. An explicit provision is now introduced on recharge due to water

conservation structures. Ground water levels has been made an integral part of

ground water assessment and categorisation of areas for ground water development

is now based on stage of ground water development and long term trend of these

levels. Allocation for domestic and industrial water supply is now recommended

based on population density and relative load on ground water for this purpose.

The report also recommends constitution of a Standing Committee -

"Research and Development Advisory Committee on Ground Water Estimation" to

provide required research and development support in the field of ground water

resource assessment.

This report is the ultimate culmination of the efforts of the members of the

committee and other experts in the field of ground water who have made significant

contribution in revising this methodology. The group to draft the report of this

committee has done a laudable job in not only preparing the draft report for

discussions of the committee members but has also finalised the same after

modifications as desired by them. I would like to express my appreciation to Shri

Santosh Kumar Sharma, Member Secretary and Regional Director, Central Ground

Water Board who with his untiring efforts and significant contributions has ably

assisted the committee in preparing this report. It is hoped that the recommendations

of the committee would be followed by different states for reassessing the ground

water resources on realistic basis.

(ARUN KUMAR)

Chairman & Addl.Secretary

Central Ground Water Board

Ministry of Water Resources

Government of India

CONTENTS 1. Chapter 1 - Introduction 1 1.1 Background 1 1.2 Composition of the Committee 2 1.3 Terms of Reference 5 1.4 Proceedings of the Committee 6 2. Chapter 2 - National scenario of ground water 8 2.1 Hydrogeological setup 8 2.2 Porous rock formations 8 2.2.1 Unconsolidated formations 8 2.2.2 Semi-consolidated formations 9 2.3 Hard rock formations 9 2.3.1 Consolidated formations 9 2.3.2 Igneous and metamorphic rocks excluding volcanic and carbonate rocks 10 2.3.3 Volcanic rocks 10 2.3.4 Carbonate rocks 11 2.4 Ground water quality 11 2.5 Ground water resource potential 11 2.6 Ground water development scenario 12 2.7 National water policy on ground water development 12 3. Chapter 3 - Recommendations of the ground water estimation Committee (1984) 14 3.1 Review of ground water resource assessment methodologies 14 3.2 Recommendations of GEC (1984) 15 3.2.1 Ground water level fluctuation and specific yield method 15 3.2.2 Normalisation of rainfall recharge 16 3.2.3 Rainfall infiltration method 17 3.2.4 Recharge from other sources 18 3.2.5 Annual ground water recharge 18 3.2.6 Potential recharge in specific situations 19 3.2.7 Total ground water resources 19 3.2.8 Ground water draft 20 3.2.9 Categorization of areas based on level of ground water development 20 3.2.10 Norms of development for various types of structures 20

3.2.11 Computation of ground water resources in confined aquifer 23 3.2.12 Static ground water resources 23 4. Chapter 4 - Review of ground water estimation methodology (1984) and recent case studies 25 4.1 Introduction 25 4.2 Merits of existing methodology 25 4.3 Limitations of existing methodology 26 4.3.1 Unit for ground water recharge assessment 26 4.3.2 Delineation of areas within a unit 26 4.3.3 Season-wise assessment of ground water resource 27 4.3.4 Ground water resource estimate in confined aquifer 27 4.3.5 Estimation of specific yield 27 4.3.6 Ground water draft estimation 28 4.3.7 Ground water flow 28 4.3.8 Return flow from ground water draft 29 4.4 Improvements in existing methodology 29 4.5 Revision of norms for ground water assessment 30 4.5.1 Case studies of ground water assessment 31 4.6 Ground water development 32 5. Chapter 5 - Recommendations on ground water resource estimation methodology 33 5.1 Introduction 33 5.2 Ground water balance equation 33 5.3 Unit for ground water recharge assessment 34 5.4 Delineation of subareas in the unit 35 5.5 Season-wise assessment of ground water resources 36 5.6 Ground water assessment in non-command area 37 5.6.1 Methodology 37 5.6.2 Ground water level fluctuation method 37 5.6.2.1 Estimation of normal recharge during monsoon season 41 5.6.2.2 Estimation of normal recharge during non-monsoon season 45 5.6.3 Recharge assessment based on rainfall infiltration factor 46 5.6.4 Total annual recharge 47

5.7 Ground water assessment in command area 47 5.7.1 Methodology 47 5.7.2 Ground water level fluctuation method 47 5.7.2.1 Estimation of normal recharge during non-monsoon season 50 5.7.3 Recharge assessment based on rainfall infiltration factor 51 5.7.4 Total annual recharge 51 5.8 Ground water assessment in saline areas and water level depletion zones 52 5.8.1 Saline areas 52 5.8.2 Water level depletion zones 52 5.9 Norms for estimation of recharge 53 5.9.1 Norms for specific yield 53 5.9.2 Recharge from rainfall 54 5.9.3 Recharge due to seepage from canals 55 5.9.4 Return flow from irrigation 55 5.9.5 Recharge from storage tanks and ponds 56 5.9.6 Recharge from percolation tanks 56 5.9.7 Recharge due to check dams and nala bunds 56 5.10 Ground water potential 56 5.10.1 Net annual ground water availability 56 5.10.2 Allocation of ground water resource for utilisation 57 5.11 Categorisation of areas for ground water development 58 5.11.1 Stage of ground water development 58 5.11.2 Long term ground water trend 58 5.11.3 Categorisation of areas for ground water development 59 5.12 Development of ground water potential 60 5.12.1 Estimation of ground water draft 60 5.12.2 Development of ground water 61 5.13 Apportioning of ground water assessment from watershed to development unit 64 5.14 Micro level study for critical areas and over-exploited areas 64 5.15 Additional potential recharge under specific conditions 65 5.15.1 Waterlogged and shallow water table areas 65 5.15.2 Flood prone areas 67 5.16 Static ground water resource 67 5.17 Confined aquifer 67 5.18 Summary report of ground water assessment 68

6. Chapter 6 - Future Strategies 72 6.1 Refinements to the recommended methodology 72 6.1.1 Introduction 72 6.1.2 Geographic unit for assessment 72 6.1.3 Employing remote sensing techniques 73 6.1.4 Computerisation of the ground water resource estimation methodology 73 6.1.5 Data monitoring 74 6.1.6 Norms for estimation of recharge 74 6.1.7 Distributed parameter modelling 74 6.2 Alternative methodology 75 6.2.1 Introduction 75 6.2.2 Soil water balance method 76 6.3 Recommendations 78 6.3.1 Introduction 78 6.3.2 Formation of standing Committee 78 ANNEXURE 1 82 ANNEXURE 2 84 ANNEXURE 3 87

1

CHAPTER 1

INTRODUCTION

1.1 BACKGROUND Quantification of the ground water recharge is a basic pre-requisite for efficient

ground water resource development and this is particularly vital for India with widely

prevalent semi arid and arid climate. The soil and water resources are limited often

being in a delicate balance. For rapidly expanding urban, industrial and agricultural

water requirement of the country, ground water utilization is of fundamental importance.

Reliable estimation of ground water resource, is therefore, a prime necessity.

Quantification of ground water resources is often critical and no single

comprehensive technique is yet identified which is capable of estimating accurate

ground water assessment. The complexities of the processes governing occurrence and

movement of ground water make the problem of ground water assessment somewhat

difficult, mainly because not only enormous data is to be procured, but a multidisciplinary

scientific approach is to be adopted for space and time location of ground water, in

quantity as well as quality. Ground water being a replenishable resource, its proper and

economic development on a sustainable basis requires its realistic assessment.

Ground water resource estimation must be seen as an interactive procedure.

Initial estimates are revised and refined by comparing these to results of other methods

and ultimately with its field manifestation. The methodologies adopted for computing

ground water resources have undergone a continuous change and adohocism adopted

earlier have given way to definite field tested norms. The computation methods, like the

ground water resources itself, have been dynamic in nature and gradual refinement has

taken place with the generation of more and more data input and with better

understanding of science of ground water.

At present, the methodology recommended by Ground Water Estimation

Committee in 1984 (GEC 1984) is being adopted to compute the ground water

resources of the country in volumetric terms. After 1984, the Central Ground Water

Board, State Ground Water Organizations, Universities and other Organizations have

undertaken a number of studies on ground water assessment. The data generated from

these studies indicate the necessity to modify the prevalent methodology. The National

2

Water Policy too enunciates periodic reassessment of ground water resources on a

scientific basis.

1.2 COMPOSITION OF THE COMMITTEE With the above background in view, the Ministry of Water resources, Government

of India constituted a committee to review and revise the Ground Water Resource

Estimation Methodology and to look into related issues (Annexure 1). The committee

consisted of the following Members :

1. Chairman, Central Ground Water Board Chairman

2. The Commissioner (CAD&MI), Member

Government of India,

Ministry of Water Resources,

Krishi Bhawan, New Delhi - 110 001.

3. Member (Survey, Assessment and Monitoring), Member

Central Ground Water Board,

NH IV, Faridabad - 121 001 (Haryana)

4. The General Manager, Member

National Bank for Agriculture

& Rural Development (NABARD)

Sterling Centre, Shivsagar Estate,

Dr. Annie Besant Road,

Post Box No. 6552, Mumbai - 400 018

5. Smt. Krishna Bhatnagar, Member

Principal Secretary to Govt./

Shri D.C. Sharma, Chief Hydrogeologist,

Government of Rajasthan,

Ground Water Department, Jodhpur (Rajasthan).

6. The Director, Member

State Water Investigation Dte,

Govt. of West Bengal, Calcutta (WB)

7. The Chief Engineer (SG&SWRGC) Member

Govt. of Tamil Nadu,

Water Resources Organisation,

3

Public Works Department,

Chennai - 600 009 (Tamil Nadu).

8. Dr. M.K. Khanna, Member

Superintending Geohydrologist,

Government of Madhya Pradesh,

Ground Water Survey Circle,

Bhopal (MP).

9. Shri S.C. Sharma, Member

Director,

Govt. of Gujarat,

Ground Water Resource Dev. Corpn.,

Near Bij Nigam, Sector-10A,

Gandhinagar (Gujarat).

10. Dr. S.N. Shukla, Member

Principal Secretary (Irrigation)

Govt. of Uttar Pradesh,

Secretariat, Lucknow (UP).

11. Dr. P. Babu Rao, Member

Director,

Ground Water Department,

B.R.K.R. Govt. Office Complex,

7th & 8th Floor, B-Block Tank Bund Road,

Hyderabad - 500 029.

12. The Director, Member

Govt. of Maharashtra,

Ground Water Survey and Dev. Agency,

PMT Building, Shankar Seth Road,

Swar Gate, Pune - 411 037 (MAHA).

13. Dr. Prem Shankar, Member

Director,

Govt. of Bihar,

GW & MI Development,

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Mithapur Agriculture Farm,

Patna (Bihar).

14. Shri J.K. Batish, Member

Research Officer

in Ground Water Cell,

Agricultural Department,

Govt. of Haryana SCO-3,

Sector-17 E, Chandigarh.

15. Dr. Gurcharan Singh, Member

Jt. Director Agriculture

(Hydrogeology),

Agriculture Department,

Govt. of Punjab, Chandigarh.

16. Dr. G.C. Mishra, Member

Scientist F Incharge Ground Water,

National Institute of Hydrology,

Jal Vigyan Bhawan, Roorkee - 247 667.

17. Dr. D. Kashyap, Member

Professor,

Department of Hydrology,

University of Roorkee,

Roorkee - 247 667. (UP).

18. Dr. S.P. Rajagopalan, Member

Head of Computer Application Div.,

Centre for Water Resources

Dev. and Management, (P.B. No. 2),

Kunnamangalam, (MBR),

Kozhikode - 673 571 (Kerala).

19. Dr. K. Sridharan, Member

Prof. of Civil Engineering,

Indian Institute of Science,

Bangalore - 560 012. (Karnataka)

20. Shri Nabi Hassan, Member

5

Director,

Ground Water Dept. Uttar Pradesh,

9th Floor, Indira Bhawan,

Ashok Market, Lucknow (U.P.).

21. Dr. P.R. Reddy, Member

Head. (Vide MOWR

Geology Division, letter dated

National Remote Sensing Agency, 3.7.1996)

Balanagar, Hyderabad - 500 037,

(Andhra Pradesh).

22. Shri Santosh K. Sharma, Member

Director, Secretary

Central Ground Water Board,

Jamnagar House, Mansingh Road,

New Delhi - 110011.

1.3 TERMS OF REFERENCE The terms of reference of this Committee are as follows :

1. To make an assessment of the scientific work done in the field with a view to

replacing, firming up or updating the various parameters and their values currently used

in the assessment of ground water resources.

2. To look into the details of the methodology recommended by Ground Water

Estimation Committee (1984) and to suggest aspects which call for a revision. The

Committee may, if considered necessary, update the existing or recommend a new

methodology for the assessment of ground water resources in different hydrogeological

situations and climatic zones.

3. To recommend norms for various parameters applicable to different geological

formations and climatic and agricultural belts, etc. which should be precisely adopted for

better assessment of the resources.

4. To recommend the smallest hydrogeological and/or administrative unit required

to be adopted for assessment of ground water resources.

5. Any other aspects relevant to the terms referred to above.

6

The Committee was to submit its report within a period of 6 months from the date

of issue of resolution. Subsequently, the period of the committee was extended up to

31/10/1996.

1.4 PROCEEDINGS OF THE COMMITTEE After the constitution of the Committee, letters were addressed to Members of

the Board of CGWB, State Ground Water Organizations, senior officers of CGWB,

scientific and research organizations dealing with ground water, universities, NABARD

and other experts to elicit their views on ground water estimation. The response from

them was overwhelming and detailed comments and views were received suggesting

various changes in the methodology. Based on these views an Approach Paper on

Revision of Ground Water Estimation Methodology was prepared for consideration of

the Committee. The list of the major contributors is given in Annexure 2.

The first meeting of the Committee was held on 14.02.1996 under the

Chairmanship of Dr. R.K. Prasad, Chairman, CGWB. The Committee, after reviewing

the Approach Paper, decided to constitute the following four sub groups.

(i) Sub-Group for recommending norms of parameters to be used in ground water

resource assessment

1. Dr. K. Sridharan - Convener

2. Director, GSDA, Pune - Member

3. Dr. Gurcharan Singh - Member

4. Dr. D.C. Sharma - Member

5. Director, SWID, Calcutta - Member

6. Engineer-in-Chief (Mech.) Irrigation Deptt., U.P - Member

(ii) Sub-Group for methodology for computation of ground water resource assessment

1. Shri N.R. Tankhiwale - Convener

2. Dr. S.P. Rajagopalan - Member

3. Shri S.C. Sharma - Member

4. Dr. D. Kashyap - Member

5. Shri Santosh K. Sharma - Member

(iii) Sub-Group on alternative methods for ground water resource assessment

1. Dr. G.C. Mishra - Convener

2. Dr. S.P. Rajagopalan - Member

3. Dr. D. Kashyap - Member

4. Shri N. Kittu - Member

7

(iv) Sub-Group on ground water withdrawal and suggestion for development strategies

1. Dr. P. Babu Rao - Convener

2. Chief Engineer (SG&SWRGC), Chennai - Member

3. Dr. Prem Shankar - Member

4. Shri J.K. Batish - Member

5. Dr. M.K. Khanna - Member

The second Meeting of the Committee was convened on 19.07.96 under the

Chairmanship of Shri Arun Kumar, Additional Secretary (WR) and Chairman, CGWB.

The reports of the Sub Groups were presented during this meeting and were discussed.

It was decided during the meeting to constitute a Group for Drafting the Report of the

Committee consisting of the following members :

1. Dr. K. Sridharan - Convener

2. Sri. N.R. Tankhiwale - Member

3. Dr. S.P. Rajagopalan - Member

4. Dr. Gurcharan Singh - Member

5. Sri. Santosh Kumar Sharma - Member Secretary

The group finalised its report after two meetings and the draft report was

circulated to all the members of the Committee for their views. The third meeting of the

Committee was held on 25th October, 1996. The draft report of Ground water

Resource Estimation Committee - 1997 was discussed in detail during the fourth

meeting held on 14th May 1997. The views expressed by the members for revised

methodology were considered and necessary modifications wherever needed were

made and report of the Committee finalised.

8

CHAPTER 2

NATIONAL SCENARIO OF GROUND WATER

2.1 HYDROGEOLOGICAL SETUP India is a vast country with varied hydrogeological situations resulting from diversified geological, climatological and topographic setups. The rock formations,

ranging in age from Archaean to Recent, which control occurrence and movement of

ground water, widely vary in composition and structure. Physiography varies from

rugged mountainous terrains of Himalayas, Eastern and Western Ghats and Deccan

plateau to the flat alluvial plains of the river valleys and coastal tracts, and the aeolian

deserts in western part. Similarly rainfall pattern also shows region-wise variations.

The following categories have been evolved to describe the ground water

characteristics of various rock types occurring in the country :

1. Porous rock formations (a) Unconsolidated formations. (b) Semi - consolidated formations.

2. Hard rock/consolidated formations

2.2 POROUS ROCK FORMATIONS 2.2.1 Unconsolidated formations The sediments comprising newer alluvium, older alluvium and coastal alluvium are by and large the important repositories of ground water. These are essentially

composed of clay, sand, gravel and boulders, ferruginous nodules, kankar (calcareous

concretions), etc. The beds of sand and gravel and their admixtures form potential

aquifers. The aquifer materials vary in particle size, rounding and in their degree of

assortion. Consequently, their water yielding capabilities vary considerably. The coastal

aquifers show wide variation in the water quality both laterally and vertically.

The piedmont zone of the Himalayas is skirted at some places by artesian

aquifers under free flowing conditions extending from Jammu and Kashmir in the west to

Tripura in the east. The hydrogeological conditions and ground water regime in Indo-

Ganga-Brahmaputra basin indicate the existence of large quantities of fresh ground

water at least down to 600 m or more below land surface, for large scale development

through heavy duty tubewells. Bestowed with high rainfall and good recharge

conditions, the ground water gets replenished every year in these zones. The alluvial

9

aquifers to the explored depth of 600 m have transmissivity values from 250 to 4000

m2/day and hydraulic conductivity from 10 to 800 m/day. The well yields range upto 100

litres per second (lps) and more, but yields of 40-100 lps are common.

2.2.2 Semi-consolidated formations The semi-consolidated formations are chiefly composed of shales, sandstones and limestones. The sedimentary deposits belonging to Gondwana and tertiary

formations are also included under this category. The sandstones form highly potential

aquifers locally, particularly in Peninsular India. Elsewhere they have only moderate

potential and in places they yield meagre supplies. These sediments normally occur in

narrow valleys or structurally faulted basins. Though these formations have been

identified to possess moderate potential, the physiography of the terrain, normally

restricts exploitation. Under favourable situations, these sedimentaries give rise to

artesian conditions as in parts of Godavari valley, Cambay basin and parts of west

coast, Pondichery and Neyveli in Tamil Nadu. Potential semi-consolidated aquifers

particularly those belonging to Gondwanas and Tertiaries have transmissivity values

from 100 to 2300 m2/day and the hydraulic conductivity from 0.5 to 70 m/day. Generally

the well yields in productive areas range from 10 to 50 lps. Lathi sandstone and Nagaur

sandstone in Rajasthan and Tipam sandstone in Tripura State also form productive

aquifers.

2.3. HARD ROCK FORMATIONS 2.3.1 Consolidated formations The consolidated formations occupy almost two thirds of the country. From the hydrogeological point of view, the consolidated rocks are broadly classified into the

following three types :

a) Igneous and metamorphic rocks excluding volcanic and carbonate rocks

b) Volcanic rocks

c) Carbonate rocks

The nature, occurrence and movement of ground water in these formations are

described below.

2.3.2 Igneous and metamorphic rocks excluding volcanic and carbonate rocks

10

The most common rock types are granites, gneisses, charnockites, khondalites,

quartzites, schist and associated phyllite, slate etc. These rocks possess negligible

primary porosity but are rendered porous and permeable due to secondary porosity by

fracturing and weathering.

Ground water yield also depends on rock types. Granite and gneiss are better

sources than charnockite. The ground water studies carried out in the crystalline hard

rocks reveal the existence, along certain lineaments, of deeply weathered and fractured

zones, locally forming potential aquifers. These lineament zones are found to be highly

productive for construction of borewells.

In areas underlain by hard crystalline and metasedimentaries viz. granite, gneiss,

schist, phyllite, quartzite, charnockite etc., occurrence of ground water in the fracture

system has been identified down to a depth of 100m and even upto 200m locally. In

most of the granite/gneiss area, the weathered residium serves as an effective ground

water repository. It has been noted that the fracture systems are generally hydraulically

connected with the overlying weathered saturated residium. The yield potential of the

crystalline and metasedimentary rocks shows wide variations. Bore wells tapping the

fracture systems generally yield from less than 1 lps to 10 lps. The transmissivity value

of the fractured rock aquifers vary from 10 to 500 m2/day and the hydraulic conductivity

varies from 0.1 to 10m/day.

2.3.3 Volcanic rocks The basaltic lava flows are mostly horizontal to gently dipping. Ground water occurrence in them is controlled by the contrasting water bearing properties of different

lava flows. The topography, nature and extent of weathering, jointing and fracture

pattern, thickness and depth of occurrence of vesicular basalts are the important factors

which play a major role in the occurrence and movement of ground water in these rocks.

Basalts or Deccan Traps usually have medium to low permeabilities depending on the

presence of primary and secondary porosity. Pumping tests have shown that under

favourable conditions, bore wells yield about 3 to 6 lps at moderate drawdowns.

Transmissivity values of these aquifers is generally in the range of 25 to 100m2 /day

and the hydraulic conductivity varies from 0.05 to 15m/day.

2.3.4 Carbonate rocks

11

Carbonate rocks include limestone, marble and dolomite. Among the carbonate rocks, limestones occur extensively. In the carbonate rocks, solution cavities lead to

widely contrasting permeability within short distances. Potential limestone aquifers are

found to occur in Rajasthan and Peninsular India in which the yields range from 5 to 25

lps. Large springs exist in the Himalayan region in the limestone formations.

2.4 GROUND WATER QUALITY The ground water in most of the areas in the country is fresh. Brackish ground

water occurs in the arid zones of Rajasthan, close to coastal tracts in Saurashtra and

Kutch, and in some zones in the east coast and certain parts in Punjab, Haryana,

Western UP etc., which are under extensive surface water irrigation. The fluoride levels

in the ground water are considerably higher than the permissible limit in vast areas of

Andhra Pradesh, Haryana and Rajasthan and in some places in Punjab, Uttar Pradesh,

Karnataka and Tamil Nadu. In the north-eastern regions, ground water with iron content

above the desirable limit occurs widely. Pollution due to human and animal wastes and

fertilizer application have resulted in high levels of nitrate and potassium in ground water

in some parts of the country. Ground water contamination in pockets of industrial zones

is observed in localised areas. The over-exploitation of the coastal aquifers in the

Saurashtra and Kutch regions of Gujarat has resulted in salinisation of coastal aquifers.

The excessive ground water withdrawal near the city of Chennai has led to sea water

intrusion into coastal aquifers.

2.5 GROUND WATER RESOURCE POTENTIAL The total annual replenishable ground water resource is about 43 million hectare metres (Mham). After making a provision of 7 Mham for domestic, industrial and other

uses, the available ground water resource for irrigation is 36 Mham, of which the

utilisable quantity is 32.5 Mham. The utilisable irrigation potential has been estimated as

64 million hectares (Mha) based on crop water requirement and availability of cultivable

land. Out of this, the potential from natural rainfall recharge is 50.8 Mha and

augmentation from irrigation canal systems is 13.2 Mha. The irrigation potential created

from ground water in the country till 1993 is estimated as 35.4 Mha.

Inspite of the national scenario on the availability of ground water being

favourable, there are pockets in certain areas in the country that face scarcity of water.

This is because the ground water development over different parts of the country is not

uniform, being quite intensive in some areas resulting in over-exploitation leading to fall

in water levels and even salinity ingress in coastal areas. The declining water levels

12

have resulted in failure of wells or deepening of extraction structures leading to

additional burden on the farmers.

Out of 4272 blocks in the country (except Andhra Pradesh, Gujarat and

Maharashtra where ground water resource assessment has been carried out on the

basis of mandals, talukas and watersheds respectively), 231 blocks have been

categorised as Over-exploited where the stage of ground water development exceeds

the annual replenishable limit and 107 blocks are Dark where the stage of ground

water development is more than 85%. Besides, 6 mandals have been categorised as

Over-exploited and 24 as Dark out of 1104 mandals in Andhra Pradesh. Similarly out

of 184 talukas in Gujarat, 12 are Over-exploited and 14 are Dark and out of 1503

watersheds in Maharashtra, 34 are Dark.

2.6 GROUND WATER DEVELOPMENT SCENARIO During the past four decades, there has been a phenomenal increase in the growth of ground water abstraction structures due to implementation of technically viable

schemes for development of the resource, backed by liberal funding from institutional

finance agencies, improvement in availability of electric power and diesel, good quality

seeds, fertilisers, government subsidies, etc. During the period 1951-92, the number of

dugwells increased from 3.86 million to 10.12 million, that of shallow tubewells from

3000 to 5.38 million and public bore/tubewells from negligible to 68000. The number of

electric pumpsets has increased from negligible to 9.34 million and the diesel pump sets

from 66,000 to about 4.59 million. There has been a steady increase in the area

irrigated from ground water from 6.5 Mha in 1951 to 35.38 Mha in 1993. During VIII

plan, it is anticipated that 1.71 million dugwells, 1.67 million shallow tubewells and

11,400 deep tubewells would be added. Similarly number of electric pumpsets and

diesel pumpsets is expected to rise by 2.02 million and 0.42 million respectively. Such a

magnitude of ground water development requires realistic assessment of ground water

resources to avoid any deleterious effects on ground water regime and to provide

sustainability to the ground water development process.

2.7 NATIONAL WATER POLICY ON GROUND WATER DEVELOPMENT The National Water Policy adopted by the Government of India in 1987 regards water as one of the most crucial elements in developmental planning. It emphasizes

that the efforts to develop, conserve, utilise and manage this resource have to be guided

by national perspective. Water is a scarce and precious national resource to be

13

planned, developed and conserved as such and on an integrated and environmentally

sound basis.

The National Water Policy enunciates the following guidelines for ground water.

There should be a periodic reassessment on scientific basis of the ground water potential, taking into consideration the quality of the water available

and economic viability.

Exploitation of ground water resources should be so regulated as not to exceed the recharge possibilities, as also to ensure social equity. Ground

water recharge projects should be developed and implemented for

augmenting the available supplies.

Integrated and coordinated development of surface water and ground water and their conjunctive use should be envisaged right from the project

planning stage and should form an essential part of the project.

Over-exploitation of ground water should be avoided near the coast to prevent ingress of sea water into fresh water aquifers.

The present action of revising the ground water estimation methodology is a

sequel to the tenets of the National Water Policy for periodic reassessment of ground

water potential on scientific basis.

14

CHAPTER 3

RECOMMENDATIONS OF THE GROUND WATER ESTIMATION

COMMITTEE (1984)

3.1 REVIEW OF GROUND WATER RESOURCE ASSESSMENT METHODOLOGIES

Attempts have been made from time to time by various Working

Groups/Committees/Task Force, constituted by Government of India to estimate the

ground water resources of the country based on status of available data and in response

to developmental needs. But, due to paucity of scientific data and incomplete

understanding of the parameters involved in recharge and discharge processes, all

these early estimations were tentative and at best approximation.

In 1972, guidelines for an approximate evaluation of ground water potential was

circulated by the Ministry of Agriculture, Government of India to all the State

Governments and financial institutions. The guidelines recommended norms for ground

water recharge from rainfall and from other sources.

The first attempt to estimate the ground water resources on a scientific basis was

made in 1979. A High Level Committee, known as Ground Water Over Exploitation

Committee was constituted by the then Agriculture Refinance and Development

Corporation (ARDC). The committee was headed by the Chairman, CGWB and

included as its members representatives from the state ground water organizations and

financial institutions. This Committee recommended definite norms for ground water

resources computations.

In the year 1982, Government of India constituted Ground Water Estimation

Committee (GEC) with the members drawn from various organizations engaged in

hydrogeological studies and ground water development. In 1984 this Committee, after

reviewing the data collected by central and state agencies, research organisations,

universities, etc. recommended the methods for ground water recharge estimation. The

recommendations of this Committee are summarised in this chapter.

3.2 RECOMMENDATIONS OF GEC (1984)

15

GEC(1984) recommended two approaches for ground water resource

assessment, namely (1) ground water level fluctuation and specific yield method and (2)

rainfall infiltration method.

3.2.1 Ground water level fluctuation and specific yield method The water table fluctuation and specific yield approach has been recommended for recharge estimation.

Generally, a well hydrograph follows a definite trend like stream hydrograph with

a peak followed by a recession limb. The recession limb in a post-recharge period is

characterised by two distinct slopes-one a steep one (from August to

October/November) and other a gentler one (from October/November to June). The

steeper limb signifies the quick dissipation of a major part of recharge during the later

part of recharge period itself. This recession of water table is sluggish in alluvial areas

compared to hard rock areas wherein a substantial recession occurs within one or one

and half month after the peak water level is achieved.

Due to less demand and adequate soil moisture in later half of recharge period

and under prevailing agricultural practice in India, the fast receding limb of hydrograph is

not considered for computation of utilisable recharge. The utilisable recharge is

estimated based on pre-monsoon (April-May) to post-monsoon (November ) water level

fluctuation for the areas receiving South-west monsoon. Similarly for the areas receiving

North-east monsoon water level fluctuations of pre-monsoon (November) and post-

monsoon (March) have been taken into consideration.

The monitoring of water level network stations needs to be adequate in space

and time and analysis of data carried out keeping in view the hydrogeological situation.

The inconsistencies in observations which may arise due to varied hydrogeological

factors should be smoothened out.

The specific yield values of the geological formations in the zone of water table

fluctuation as computed from pumping tests are to be utilized in the recharge estimation.

As a guide following values computed in different studies are recommended :

(I) Sandy alluvial area 12 to 18 percent

(ii) Valley fills 10 to 14 percent

(iii) Silty/Clayey alluvial area 5 to 12 percent

(iv) Granites 2 to 4 percent (v) Basalts 1 to 3 percent

(vi) Laterite 2 to 4 percent

16

(vii) Weathered Phyllites, Shales, 1 to 3 percent

Schist and associated rocks.

(viii) Sandstone 1 to 8 percent

(ix) Limestone 3 percent

(x) Highly Karstified Limestone 7 percent

3.2.2 Normalisation of rainfall recharge The water table fluctuation in an aquifer corresponds to the rainfall of the year of observation. The rainfall recharge estimated should be corrected to the long term

normal rainfall for the area as given by India Meteorological Department.

For calculating the annual recharge during monsoon the formula indicated below

may be adopted.

Monsoon Recharge = (S + DW - Rs - Rigw - Ris) Normal Monsoon RfAnnual Monsoon Rf

Rs + Ris +where,

S = change in ground water storage volume during pre and post monsoon period

(April/May to November), (million cubic metre or mcm) obtained as below:-

Area (sq.km.) x Water level fluctuation (m) x Specific yield

The areas not suitable for recharge like high hilly and saline area should be excluded.

DW = gross ground water draft during monsoon (mcm)

Rs = recharge from canal seepage during monsoon (mcm).

Rigw = recharge from recycled water from ground water irrigation during monsoon

(mcm).

Ris = recharge from recycled water from surface water irrigation during monsoon

(mcm)

RF = rainfall (metre).

To eliminate the effects of drought or surplus rainfall years, the recharge during

monsoon is estimated as above for a period of 3 to 5 years and an average figure is

taken for long term recharge. Recharge from winter rainfall may also be estimated on

the same lines.

3.2.3 Rainfall infiltration method In areas where ground water level monitoring is not adequate in space and time, rainfall infiltration may be adopted. The norms for rainfall infiltration contributing to

ground water recharge are evolved, based on the studies undertaken in various water

17

balance projects in India. The norms for recharge from rainfall under various

hydrogeological situations are recommended in the following table.

Table : Rainfall infiltration factor in different hydrogeological situations

S.No

Hydrogeological situation Rainfall infiltration factor

1 Alluvial areas

a. Sandy Areas 20 to 25 percent of normal rainfall

b. Areas with higher clay content 10 to 20 percent of normal rainfall

2 Semi-Consolidated Sandstones

(Friable and highly porous) 10 to 15 percent of normal rainfall

3 Hard rock area

a. Granitic Terrain

(i) Weathered and Fractured 10 to 15 percent of normal rainfall

(ii) Un-Weathered 5 to 10 percent of normal rainfall

b. Basaltic Terrain

(I) Vesicular and Jointed Basalt 10 to 15 percent of normal rainfall

(ii) Weathered Basalt 4 to 10 percent of normal rainfall

c. Phyllites, Limestones, Sandstones, 3 to 10 percent of normal rainfall

Quartzites, Shales, etc.

The normal rainfall figures are taken from India Meteorological Department which

is main agency for collection and presentation of rainfall data. The ranges of rainfall

infiltration factor are recommended as a guideline and need to be adopted based on

their applicability to prevalent hydrogeological situation. Besides natural ground water

recharge estimation, recharge due to seepage from canals, return seepage from

irrigated fields, seepage from tanks and lakes, potential recharge in water logged and

flood prone areas are computed based on following recommended norms.

3.2.4 Recharge from other sources

Recharge due to seepage from canals The following norms may be adopted in most of the areas except where realistic

values have been arrived at, from project studies.

(i) For unlined canals in normal type of soil with some clay content along with sand :-

18

15 to 20 ham/day/106 sq.m of wetted area of canal

(ii) For unlined canals in sandy soils :-

25 to 30 ham/day/106 sq.m of wetted area

(iii) For lined canals, the seepage losses may be taken as 20 percent of the above

values.

Return seepage from irrigation fields (i) Irrigation by surface water sources

(a) 35% of water delivered at the outlet for application in the field. The variation in

percentage of seepage may be guided by studies undertaken in the area or in a

similar area.

(b) 40% of water delivered at outlets for paddy irrigation only.

(ii) Irrigation by ground water sources

(a) 30% of the water delivered at outlet. For paddy irrigation 35% as return seepage of

the water delivered may be taken.

In all the above cases, return seepage figures include losses in the field channel

also and these should not be accounted for separately.

Seepage from tanks The seepage from the tanks may be taken as 44 to 60cm per year over the total

water spread. The seepage from percolation tanks is higher and may be taken as 50%

of its gross storage. In case of seepage from ponds and lakes, the norms as applied to

tanks may be taken.

3.2.5 Annual ground water recharge The annual replenishable ground water recharge includes the following

components :

Total annual recharge = Recharge during monsoon + Non-monsoon rainfall recharge

+ Seepage from canals + Return flow from irrigation + Inflow

from influent rivers etc. + Recharge from submerged lands,

lakes etc.

3.2.6 Potential recharge in specific situations Besides the estimation of normal recharge, the methodology recommends

computation of potential recharge in shallow water table areas/waterlogged areas and in

flood prone areas.

Potential resource in water logged area and shallow water table zones

19

Potential ground water resource = (5 - B) X A X Specific Yield

where

B = depth to water table below ground surface in pre-monsoon period in shallow

aquifers (m)

A = area of shallow water table zone (m2)

The planning of minor irrigation works in the areas indicated above should be

done in such a way that there are no long term adverse effects on water table. The

behaviour of water table in the adjoining area which is not waterlogged should be taken

as a guide for development purposes.

The potential recharge from flood plains may be estimated on the same norms as

for ponds and lakes, i.e., 44 to 60cm per year over the water spread area for period

equal to the retention period.

3.2.7 Total ground water resources The total ground water resources for water table aquifers is taken as annual

ground water recharge plus potential recharge in shallow water table zone.

The total ground water resource, thus computed would be available for utilization

for irrigation, domestic and industrial uses. The base flow in rivers is a regenerated

ground water resource and is some times committed for lift irrigation schemes and other

surface irrigation works. It is, therefore, recommended that 15% of total ground water

resources be kept for drinking and industrial purposes, for committed base flow and to

account for the irrecoverable losses. The remaining 85% can be utilized for irrigation

purposes. But wherever the committed base flows, domestic and industrial uses are

more than 15%, the utilisable resources for irrigation may be considered accordingly.

3.2.8 Ground water draft The ground water draft is the quantity of ground water withdrawn from the ground

water reservoirs. The total quantity withdrawn is termed as gross draft. The annual

ground water draft of a structure is computed by multiplying its average discharge and

annual working hours. The number of working hours can be calculated by the hourly

consumption of electrical or diesel energy. The ground water draft is also calculated by

the irrigation requirement of crops in the command area of the structure. For working

out ground water balance, 70% of gross extraction is taken which is known as Net

Ground Water Draft. The 30% is presumed to go as return seepage to ground water

regime.

3.2.9 Categorization of areas based on level of ground water development

20

The level of ground water development in an area is to be taken as the ratio of

net yearly draft to total utilisable ground water resources for irrigation. It can be

expressed as,

Level of ground water development Net yearly draftUtilizable resource for irrigation

= 100

For the purpose of clearance of schemes by financial institutions, categorization

of areas based on level of ground water development at year 5 has been recommended

as follows :

Category of areas Stage of ground water development (%) at Year 5

(a) White < 65% (b) Grey > 65% but < 85% (c) Dark > 85% but < 100%

In dark areas, micro-level surveys are required to evaluate the ground water

resources more precisely for taking up further ground water development.

3.2.10 Norms of development for various types of structures The norms/yardsticks of area irrigated from various types of ground water minor

irrigation units in different states as indicated by them are given below.

S.No

.

Type of Minor Irrigation work Area Irrigated (ha.)

1. Andhra Pradesh

Dugwell with mhot 0.5

Dugwell with pump set 2.0

Private tubewell 4.0

2. Bihar

Dugwell without pump

(i) Upto 3m dia 0.6

(ii) From 3 to 6m dia 1.0

Dug cum borewell

Tubewell

21

(i) 10cm dia 4.0

(ii) 5cm dia 2.0

Diesel pumpset on dugwell/

Surface water sources

(i) 5 HP pump set 2.0

(ii) Pump above 5 HP 4.0

3. Haryana

Dugwell 1.2

Shallow Tubewell 4.3

4. Punjab

Dugwell 1.0

Shallow Tubewell 5.0

5. Madhya Pradesh

Dugwell 1.0

Shallow Tubewell 6.8

6. Maharashtra

Dugwell with pump set 2.0

Dugwell with mhot 0.5

S.No

.

Type of Minor Irrigation work Area Irrigated (ha.)

7. Tamil Nadu

Private Tubewell 8.0

Filter point 4.0

Boring in well 0.8

Deepening of well 0.8

8. Uttar Pradesh

Masonry well 1.0

Persian wheel (addl.) 0.5

Boring (small/marginal farmers)

addl.

0.5

22

Pump set on boring 5.0

Tubewell 5.0

9. Tripura

Shallow tubewell 4.0

Artesian well 0.5

10. West Bengal

Dugwell 0.4

Shallow Tubewell 3.0

11. Rajasthan

Dugwell 2.0

Low duty tubewell 2.0

Dug cum borewell 4.0

These areas are to be multiplied by applicable water depth to get the draft of

ground water.

The above data indicate that the norms vary from state to state depending upon

the existing agriculture practices, local hydrogeological conditions, availability of power

etc. and as such it is recommended that regional norms may be developed by the states

and Central Ground Water Board based on sample surveys. In case of Public

Tubewells, data for discharge and running hours is already available and that should be

used for computation of draft.

3.2.11 Computation of ground water resources in confined aquifer For the confined aquifers which are hydrogeologically separate from shallow water table aquifers, the ground water assessment may be done by rate concept. The

ground water available in a confined aquifer equals the rate of flow of ground water

through this aquifer. The rate of ground water flow available for development in a

confined aquifer in the area can be estimated by using Darcys law as follows :

Q = TIL

where,

Q = Rate of flow through a cross-section of aquifers in m3 /day.

T = Transmissivity in m2/day

I = Hydraulic Gradient in m/km

23

L = Average width of cross-section in km.

The transmissivity may be computed from pumping test data of tubewells.

Leakage from overlying or underlying aquifer may also be accounted for in the

calculation of ground water available for development in a confined aquifer.

The tubewell draft tapping a deeper confined aquifer may be treated separately

and may be accounted for at the time of quantitative assessment of deeper confined

aquifer. The total draft of these tubewells may be taken as gross draft of which 30

percent may be taken recycled and may be added as recharge to water table aquifers.

The utilisable recharge may be taken as 85 percent of the total ground water flow

available for development.

The computation of lateral flow in the confined aquifer may be done by flow net

analysis method by computing all the parameters reflected in Darcys formula. However,

for working out the optimum development of the confined aquifers, it is recommended

that the recharge area of the confined aquifers may be demarcated, the average annual

recharge to the confined aquifer in this recharge area estimated, and the extent of

development of this aquifer is limited to this amount of recharge indicated above.

3.2.12 Static ground water resources The quantum of water available for development is usually restricted to long term average recharge or in other words to Dynamic Resource. However, recent data

indicate that even in states with high degree of ground water development, water levels

have not shown a declining trend. It is, therefore, considered that temporary depletion of

water table taking place in drought years is made up in years of high rainfall or in other

words the utilisation of static reserves and consequent depletion in water levels in

drought years is made up during years of high rainfall. This may be studied by

comparing the long term rainfall and the water table hydrograph to establish the

periodical recharge. In such areas it would be desirable that the ground water reservoir

be drawn to the optimum limit to provide adequate scope for its recharge during the

following monsoon period. An estimate of static ground water reserve is desirable for

planning the optimum utilisation for future development of the ground water resources of

an area.

The static ground water resource in an area may be computed as below:

Static Ground Water = Thickness of the aquifer below the Areal Specific

Reserve (m3) zone of water level fluctuation (m) x extent x yield

down to exploitable limit. of the of the

24

aquifer aquifer

(m2)

The development of static resource has to be done carefully and cautiously. It is

recommended that the static ground water resource, basin wise/district wise in each

state may be evaluated. However, no development schemes based on this resource be

taken up at this stage.

25

CHAPTER 4

REVIEW OF GROUND WATER ESTIMATION

METHODOLOGY (1984) AND RECENT CASE STUDIES

4.1 INTRODUCTION Two approaches for ground water assessment are recommended by the GEC -

1984, namely: (a) ground water level fluctuation method, (b) norms of rainfall infiltration.

Improvement in the existing methodology requires a relook on the concepts and details

of the methodology, as well as an evaluation and utilisation of the case studies of ground

water assessment in the recent years in different parts of the country. While going

through such a review process, one may also keep in view the status of data on ground

water resource evaluation, as available in the country presently. The methodology as

recommended by the GEC - 1984 is reviewed here, both on its merits and limitations.

The chapter also provides a review of recent case studies on ground water assessment

in various parts of the country, and the type of data that is available, both from routine

observations and from special studies.

4.2 MERITS OF EXISTING METHODOLOGY The existing methodology outlined in Chapter 3 has some basic merits. As per

this methodology, ground water recharge is to be estimated based on ground water level

fluctuation method, as applied for the monsoon season. If adequate data of water level

observations are not available, rainfall infiltration factor norms is to be used. The basic

merits of these methods are: (a) simplicity (b) suitability of the method with regard to the

data normally available from the ground water level monitoring program of the state and

central government agencies (c) reliability and robustness of the ground water level

fluctuation method, as it is based on the well established principle of ground water

balance, and (d) provision of an alternate approach based on the rainfall infiltration

factor, in the absence of adequate data of ground water levels. It may be noted that

though the rainfall infiltration factor method is empirical, the approach provides scope

for continuous improvement, as the norms can be periodically revised and refined for

different agro-climatic and hydrogeological regions, based on case studies of ground

water assessment in different regions of the country.

26

While alternate methodologies for ground water recharge assessment are

possible, the ground water level fluctuation method, based on the concept of ground

water balance, is the most suitable and reliable at this point of time, considering the type

and extent of data available. As the ground water assessment has to be done all over

the country at each block/taluka/mandal level, there is also a need to retain the alternate

empirical approach based on specified norms, for application in areas without adequate

water level data. The two approaches recommended by the GEC - 1984 can therefore

still form the basis for ground water assessment.

4.3 LIMITATIONS OF EXISTING METHODOLOGY Several issues have been raised with regard to the methodology recommended in the GEC - 1984 Report. The limitations of the existing methodology are summarised

as follows.

4.3.1 Unit for ground water recharge assessment The GEC - 1984 does not explicitely specify the unit to be used for ground water

assessment, but it is implied in the discussions that the assessment is to be made for an

administrative unit, namely a block. While an administrative unit is convenient from

development angle, it is not a natural hydrological unit. Watershed has been proposed

as a more desirable option, and in fact, some states are presently using watershed as

the unit for ground water assessment. However, it is to be recognised that in alluvial

areas, there may be ground water flow across watershed boundary also, as surface and

subsurface water divides may not coincide. It has also been suggested that the unit for

ground water assessment should be based on geomorphological and hydrogeological

characteristics.

4.3.2 Delineation of areas within a unit The existing methodology does not take into account the spatial variability of

ground water availability within a unit. The estimation of ground water recharge as per

the GEC - 1984 has basically three components: (a) recharge from rainfall (b) recharge

from return flow from irrigation and other sources (c) potential recharge in waterlogged

and shallow water table areas. Among these, the recharge from rainfall is the only

component which is available in a distributed way over the entire block or taluka.

Recharge from return flow from surface water irrigation, is mainly relevant only to canal

command areas. In alluvial areas, some component of return flow from canal irrigation

may be available downstream of the command area, but even here, the availability is

spatially restricted. The potential recharge from waterlogged and shallow water table

27

areas can also distort the estimate of available ground water, since this recharge can be

realised only under special circumstances, and even then this water may be available

only locally. Separate assessment may also be required for areas where ground water

is saline. Hence, there is a necessity for delineation of different sub-areas within a unit

for ground water assessment.

4.3.3 Season-wise assessment of ground water resource There is a clear need expressed for season-wise assessment of the ground

water resource, for Kharif, Rabi and summer seasons or for monsoon and non-monsoon

seasons. It is felt that this approach may explain the paradox of water not being

available in summer even for drinking purposes in hard rock areas, while the stage of

ground water development as evaluated based on the GEC - 1984 recommendations

indicate good availability for development.

4.3.4 Ground water resource estimate in confined aquifer The GEC - 1984 has made a brief mention regarding ground water resource

estimation in confined aquifers, based on Darcys law. Questions have been raised on

this aspect on three grounds: (a) practical utility of this estimate (b) reliability of the

estimate, in view of the difficulty of delineating the confined and unconfined parts, or the

recharge and discharge parts (c) possibility of duplication of resource estimation as the

flow which enters the confined aquifer is already estimated under unconfied aquifer part

due to their inter-relationship. However, there may be situations in alluvial areas where

ground water estimate in confined aquifer may be an important aspect.

4.3.5 Estimation of specific yield The ground water level fluctuation method requires the use of specific yield value

as a key input for assessment of ground water recharge. The GEC - 1984 suggests that

for semicritical and critical areas, pumping tests may be used for the estimation of

specific yield. Regarding regional ground water assessment in hard rock areas,

determination of specific yield through pumping tests has several limitations. First, there

is an inherent bias in the location of test wells in terms of potential yield of the well for

future utilisation. Thus the local value may not be an average representation of the

region. Secondly, pumping tests are more useful for estimating transmissivity value than

specific yield value. Small duration pumping tests on dug wells are not suitable for the

estimation of specific yield. Third, a proper estimation of parameters (including specific

yield) from long duration pumping tests in hard rock areas, requires the use of fairly

sophisticated modelling techniques, and simplistic estimates based on Theis curve (or

28

some other simple models) may result in wrong assessment of specific yield. In alluvial

areas, pumping tests may yield more representative values of specific yield , but here

also, the tests should be of sufficiently long duration.

4.3.6 Ground water draft estimation Ground water draft refers to the quantity of ground water that is being withdrawn

from the aquifer. Ground water draft is a key input in ground water resource estimation.

Hence, accurate estimation of ground water draft is highly essential to calculate the

actual ground water balance available. The following three methods are normally used

in the country for ground water draft estimation.

(a) Based on well census data : In this method, the ground water draft is estimated by

multiplying the number of wells of different types available in the area with the unit draft

fixed for each type of well in that area. This method is being widely practiced in the

country.

(b) Based on electrical power consumed : In this method, the ground water draft

estimation is done by multiplying the number of units of power consumed for agricultural

pumpsets with that of the quantity of water pumped for unit power.

(c) Based on the ground water irrigated area statistics : In this method, the ground water

draft is estimated by multiplying the acreage of different irrigated crops (cultivated using

ground water) with that of the crop water requirement for each crop.

In the recent years, studies conducted by NRSA have shown that remote sensing

data collected from earth orbiting satellites provide information on ground water irrigated

crops and their acreage. This can form an additional or alternate method for draft

estimation in non-command area.

4.3.7 Ground water flow The ground water level fluctuation method as per the GEC - 1984 does not

account for ground water inflow/outflow from the region and also base flow from the

region, as part of the water balance. This means that the recharge estimate obtained

provides an assessment of net ground water availability in the unit, subject to the natural

loss or gain of water in the monsoon season due to base flow and inflow/outflow.

4.3.8 Return flow from ground water draft The GEC - 1984 recommends that 30% of gross ground water draft used for non-

paddy areas may be taken as return flow recharge, and this is raised to 35% for paddy

areas. It is generally felt that with respect to ground water irrigation, these estimates of

recharge from return flow are high, particularly for non-paddy areas. It is even felt that

29

when the water table is relatively deep and the intensity of ground water application is

relatively low, return flow recharge may be practically negligible. On the other hand,

some data available from Punjab, Haryana and Western UP suggests, that the return

flow from paddy areas may be higher than 35%.

4.4 IMPROVEMENTS IN EXISTING METHODOLOGY After due consideration of the limitations discussed above, several improvements are proposed in the existing methodology based on ground water level fluctuation

approach. These are as follows.

a) It is proposed that watershed may be used as the unit for ground water resource

assessment in hard rock areas, which occupy about 2/3rd of the country. The

assessment made for watershed as unit may be transferred to administrative unit such

as block, for planning developmental programmes. For alluvial areas, the present

practice of assessment based on block-wise basis is retained. The possibility of

adopting doab as the unit of assessment in alluvial areas needs further detailed studies.

b) It is proposed that the total geographical area of the unit for resource assessment be

divided into subareas such as hilly regions, saline ground water areas, canal command

areas and non-command areas, and separate resource assessment may be made for

these subareas. Variations in geomorphological and hydrogeological characteristics

may be considered within the unit.

c) A qualitative approach for assessing season-wise availability is suggested.

Directions are provided for data acquisition programme in future, for further improvement

of estimate in this regard.

d) The focus of ground water recharge assessment may be for unconfined aquifers. In

specific alluvial areas where resource from deep confined aquifer is important, such

resource may have to be estimated by specific detailed investigation, taking care to

avoid duplication of resource estimation from the upper unconfined aquifers.

e) It is proposed that for hard rock areas, the specific yield value may be estimated by

applying the water level fluctuation method for the dry season data, and then using this

specific yield value in the water level fluctuation method for the monsoon season to get

recharge. For alluvial areas, specific yield values may be estimated from analysis of

pumping tests. However, norms for specific yield values in different hydrogeological

regions may still be necessary for use in situations where the above methods are not

feasible due to inadequacy of data.

30

f) The problem of accounting for ground water inflow/outflow and base flow from a

region is difficult to solve. If watershed is used as a unit for resource assessment in

hard rock areas, the ground water inflow/outflow may become negligible. The base flow

can be estimated if one stream gauging station is located at the exit of the watershed.

g) Norms for return flow from ground water and surface water irrigation are to be revised

taking into account the source of water(ground water/surface water), type of crop

(paddy/non-paddy) and depth of ground water level.

h) The needs for drinking water and industrial water use are to be decided based on

the population density of the area.

4.5 REVISION OF NORMS FOR GROUND WATER ASSESSMENT As stated in Section 4.2, there is a need to retain the recommendation of norms

for recharge assessment for use in situations where adequate data of ground water level

is not available. However, these norms are to be periodically revised, based on the

results and observations of recent ground water assessment studies in various parts of

the country. In a large country like India, such studies are undertaken by a number of

central and state government agencies, research institutions, universities, non-

government organisations etc. These studies may be of varied quality and rigour.

Procurement and analysis of these data require considerable time. In the limited time

available for the Committee, only some of these data could be studied.

While it is reasonable to adopt a specific standardised methodology of ground

water assessment for 5 years, it is necessary to update the norms on an annual basis,

based on the results of case studies of several ground water assessment across the

country. For this, it is recommended that a Standing Committee may be formed, which

may be authorised to revise the norms periodically and circulate it to the different states.

To facilitate the work of this Standing Committee, an initial effort is first required to

prepare a data bank, comprising the results of ground water assessments made by

different central and state government agencies, research institutions, universities, non

government organizations etc. Once the initial data bank is available, updating it to

include subsequent investigations will require less effort. The Standing Committee may

evolve a format for collection of information of the data bank. In evolving the format, the

approach proposed under the Hydrology Project may be kept in view. With the

formation of a Standing Committee, it may be possible to provide norms on a state-

wise basis for different agro-climatical and hydrogeological regions, once the initial data

bank is created. However, the present Committee has made a limited review of case

31

studies of ground water assessment in the last 10 to 15 years, in order to revise the

norms for ground water assessment.

4.5.1 Case studies of ground water assessment The studies on ground water assessment in recent years can be broadly

catagorised as follows:

(a) Blockwise ground water assessment by state ground water agencies and Central

Ground Water Board, based on the recommendations of the GEC - 1984. (b) Detailed

pilot studies undertaken in specific areas by the Central Ground Water Board. (c)

Ground water assessment through computer modelling as part of the pilot studies

referred above or otherwise. (d) Recharge assessment in a number of

watersheds/basins, using the injected Tritium method, made by the National

Geophysical Research Institute. (e) Studies by National Remote Sensing Agency and

other agencies of Indian Space Research Organisation.

Normally, the results of blockwise assessment based on the ground water level

fluctuation method should have formed the basis for the revision of the norms. However,

there is a problem in using these results for the present purpose, as the estimate of

recharge is based on adhoc assumption for the value of specific yield. Revising adhoc

norms for recharge based on estimates, which themselves are based on adhoc norms

for specific yield, hardly looks appropriate. For example, for granitic terrains in

Karnataka, the recharge based on the water level fluctuation approach is estimated as

13% of rainfall, using a specific yield value of 3%. The detailed modelling studies for the

Vedavati River basin in Karnataka has indicated an average specific yield value of 2%

for similar terrains. If the latter value of specific yield is adopted and the recharge values

are revised, the recharge reduces to 8.7% instead of 13%. In view of these difficulties,

greater importance is given in the present review to ground water assessment based on

detailed pilot studies, where rigorous methods have been applied for the estimation of

both specific yield and recharge factor. The recharge estimate in different regions,

based on injected Tritium method, is also considered in revising the norms.

Annexure 3 presents a summary of results from a number of case studies, which

were reviewed. For the sake of brevity and simplicity, a standard format is used in the

presentation, providing summary information on project, source of information, period of

study, location, area, soil/rock type, methodology of assessment, estimated results for

specific yield and recharge factor. It is to be noted that such a simple presentation may

hide important data and limitations relevant to the assessment. However, in an overview

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as attempted here, consideration of finer details of individual projects is hardly feasible

and is beyond the scope of this Committee.

The case studies presented in Annexure 3 contain recharge estimates based on

the water level fluctuation approach recommended by the GEC - 1984, detailed pilot

studies where a rigourous water balance is made both for the rainy and non-rainy

seasons, studies based on computer modelling using finite difference or finite element

method, recharge estimates based on Tritium injection technique, studies based on soil

moisture measurement technique, and other miscellaneous estimates. The results

presented in Annexure 3 form the principal basis for the revised norms recommended in

this report. Besides, the comments provided by a number of agencies in response to the

request of the Central Ground Water Board form another important input.

4.6 GROUND WATER DEVELOPMENT There are two faces to ground water assessment, the estimation of ground water recharge from rainfall and other sources and the assessment of development potential.

These require an estimate of present ground water draft. Ground water draft has to be

necessarily estimated by indirect methods such as well census, electricity consumption

and area irrigated from ground water. There can be considerable uncertainties in these

estimates, unless a careful review is made for consistency from different approaches. In

planning further development based on the potential, it is necessary to review the

average ground water draft and associated irrigation command for different types of

ground water structures.

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CHAPTER 5

RECOMMENDATIONS ON

GROUND WATER RESOURCE ESTIMATION METHODOLOGY

5.1 INTRODUCTION The revised ground water resource estimation methodology as proposed by the

committee is presented in this chapter. The methodology as recommended here, may

be adopted in future for ground water resource estimation. The two approaches

recommended by the GEC - 1984, namely ground water level fluctuation method and

rainfall infiltration factor method, can still form the basis for ground water assessment.

However, several improvements are made in the basic approaches based on the

discussions presented in Sections 4.3 to 4.5. In the proposed methodology,

distinctions such as hard rock areas and alluvial areas, canal command areas and non-

command areas and recharge in monsoon season and non-monsoon season, are kept

in view. It is recommended that recharge due to rainfall in the monsoon season is to be

estimated by ground water level fluctuation method, unless adequate data is not

available, for which case rainfall infiltration factor method may be used. The ground

water recharge assessment is essentially for unconfined aquifers. The problem of

confined aquifers is separately discussed in Section 5.17. The usable ground water

resource is essentially the dynamic resource which is recharged annually by rainfall and

other sources. The concept of static ground water resource is discussed in Section

5.16.

5.2 GROUND WATER BALANCE EQUATION The water level fluctuation method is based on the application of ground water

balance equation, which is stated in general terms as follows for any specified period,

Input -Output = Storage increase (1)

In the above equation, the terms input and output are used in the general sense,

referring to all components of ground water balance, which are either input to the unit,

or output from the unit of ground water system taken up for resource assessment (ex :

watershed, block etc.). Hence input refers to recharge from rainfall and other sources

and subsurface inflow into the unit. Output refers to ground water draft, ground water

evapotranspiration, base flow to streams and subsurface outflow from the unit.

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Eqn.1 holds good for any period and hence it can be applied to the year as a

whole or to different seasons in the year separately. From ground water assessment

point of view, it is desirable to apply the equation separately for different seasons, such

as monsoon and non-monsoon seasons or kharif, rabi and summer seasons.

The right side term in eqn. 1, namely storage increase (positive for storage

increase, negative for storage decrease), is given as a function of the ground water level

change and specific yield. Hence ground water level measurements at the beginning

and end of the season form necessary input for the estimation of storage change.

The input and output terms in eqn. 1 include subsurface inflow and outflow

components across the boundary of the unit, which depend on the transmissivity and

hydraulic gradient. It is advantageous to adopt the unit for ground water assessment as

basin/subbasin/watershed, as the inflow/outflow across these boundaries may be taken

as negligible.

5.3 UNIT FOR GROUND WATER RECHARGE ASSESSMENT Watershed with well defined hydrogeological boundaries is an appropriate

hydrological unit for ground water resource estimation. In hard rock areas, the

hydrogeological and hydrological units normally coincide, which may not be the case in

alluvial areas where the aquifers traverse the basin boundaries. In hard rock areas

which occupy about 2/3rd area of the country, assessing the ground water on watershed

as a unit is more desirable. In many states where the development unit is either a block

or a taluka or a mandal, based on the ground water resource worked out on watershed

as a unit, the final assessment of ground water potential may be apportioned and

presented on block/taluka/mandal-wise basis, which would facilitate planning of

development programmes. In case of alluvial areas where it is difficult to identify

watershed considering the trans-boundary aquifer system, the present methodology of

assessing the ground water potential on block/taluka/mandal-wise basis may continue.

For purposes of classification into alluvial or hard rock areas, the predominant

hydrogeology of the unit is to be considered. Hence, localised alluvial patches occurring

in predominantly hard rock area should be considered as part of the watershed unit in

hard rock area. In the states where switch over to watershed is not possible

immediately, the present practice of assessing the ground water potential for

block/taluka/mandal may continue for sometime even for hard rock areas. However, the

state ground water departments shall endeavour to demarcate and switch over to

watershed as a unit for assessment, within a period not exceeding 5 years.

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In each unit, ground water assessment may be made once in three years.

However, the ground water draft figures can be updated every year.

5.4 DELINEATION OF SUBAREAS IN THE UNIT GEC - 1984 provides for assessment of ground water resources in an

administrative unit, namely block, without any subdivision. Treating the entire block area

as a single unit has resulted in certain distortions, wherein a block as a whole may be

categorised as a region with good potential for ground water development, but in

practice, it is possible that in a large part of the block, in the summer season, water may

be scarce even for domestic supply. This anomaly can be removed, if the ground water

assessment in a block is done, keeping in view the spatial and seasonal variability of

ground water resource. With this in view, the following recommendations are made with

regard to delineation of subareas within the unit, which may be a watershed (hard rock

areas) or a block/taluka/mandal (alluvial areas).

First, out of the total geographical area of the unit, hilly areas (slope greater than

20%) are to be identified and deleted as these are not likely to contribute to ground

water recharge. However, the local topographical and geomorphological situations such

as valley, terrace, plateau occurring within (>) 20% slope zone may be considered for

recharge computations. Out of the remaining area after deleting the hilly area, areas

where the quality of ground water is beyond the usable limits as presently decided and

practiced in the state, should be identified and handled separately. It may not be correct

to recommend a uniform quality standard for all the areas in different states, due to

variations in quality norms criteria prevalent in the use of ground water. The ground

water resource beyond the permissible quality limits has to be computed separately.

The area with brackish/saline ground water be delineated and the ground water resource

of these areas be computed separately. The remaining area after deleting the hilly area

and separating the area with poor ground water quality, is to be delineated as follows :

(a) Non-command areas which do not come under major/medium surface water

irrigation schemes.

(b) Command areas under major/medium surface water irrigation schemes.

If felt necessary, within these two types of areas, further subdivision based on

geomorphological and hydrogeological characteristics may be made.

5.5 SEASON-WISE ASSESSMENT OF GROUND WATER RESOURCES Ground water recharge assessment is to be made separately for the non-

command and command areas in the unit as delineated in Section 5.4. For each of

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these subareas, recharge in the monsoon season and non-monsoon season is to be

estimated separately. For most parts of the country receiving the main rainfall from

South west monsoon, the monsoon season would pertain to kharif period of cultivation.

In areas of the country, such as Tamil Nadu, where the primary monsoon season is the

North east monsoon, the period of monsoon season should be suitably modified. For

purposes of recharge assessment using water level fluctuation method, the monsoon

season may be taken as May/June to October/November for all areas, except those

where the predominant rainfall is in the North east monsoon season. This

recommendation means that an additional period of one month after cessation of

monsoon is taken to account for the base flow which occurs immediately following the

monsoon period, but may not be utilised for ground water development, based on

present practices. Generally, a well hydrograph follows a definite trend like stream flow

hydrograph with a peak followed by a recession limb. The recession limb in the post

monsoon period, particularly in hard rock areas, is categorised by two slopes: a steep

limb from September-October to October-November and other gentle limb from October-

November to May-June. The steeper limb indicates that whatever rise has taken place

during the monsoon period, of the total, a significant part is lost soon after the end of

rainfall. The rate of recession of the water level is relatively rapid in the beginning, for a

period of 1-11/2 months immediately after the water level rises to maximum. Due to less

demand for ground water in view of adequate moisture in soils, the resource available

during this period are not fully utilised. It is therefore, recommended that the ground

water recharge may be estimated on pre-monsoon (May-June) to post monsoon

(October-November) water level fluctuations for the areas receiving rainfall from